Radar level gauging is based on allowing electromagnetic waves propagate into a tank and be reflected by the surface of a product in the tank. The reflected signal is then received and processed in order to identify an echo, i.e. the reflection from the surface. In order to be accurate, it is important that the surface echo can be distinguished from other disturbing reflections. Such reflections may result from internal tank geometry such as flanges, stirring devices, filling nozzles, etc, or from physical properties of the product, such as turbulence, foam, etc.
Considerable effort is made to ensure that the algorithm used to identify the surface echo is successful, so that a correct level measurement is provided.
Also for other reasons it may be appropriate to provide a redundant level measurement, i.e. to handle a gauge failure of some kind. Such a failure can be e.g. a mechanical or electrical fault in the gauge.